1. Technical Field
The technology described herein is generally related to the field of electrical circuits.
2. Description of Related Art
Electrical current sensing is used in a variety of applications. For example high current demand apparatus, such as motors, generally have control circuits which use current sensing to implement control signals back to the load. FIG. 1 (Prior Art) is an electrical schematic diagram of a conventional current sense circuit 100 for setting a voltage level to a predetermined value for such apparatus operations. For example, and referring to FIG. 1 (Prior Art), measuring a current is accomplished by forcing a current through a first, sense resistor “Rsense” and measuring the voltage “V” across the sense resistor, where VMEASURED=i1·Rsense. In control circuitry, to control the current “i1” through the resistor Rsense, a feedback gain loop can be used to measure the voltage across the resistor and then adjust the current “Iset” so that the voltage is held at a predetermined value. An operational amplifier, “OP AMP,” 101 is used to represent any negative feedback gain component(s) needed to force the electrical current Iset through the sense resistor Rsense connected in parallel with a reference resistor, “Rref,” thereby forcing the same voltage drop across both resistors, Rsense, Rref. The second resistor Rref has a reference current “Iref” flowing through it. Thus, the sensed current is the value of “Iout”:Iout=(Rref÷Rsense)×Iref. The ratio of the sizes of the two resistors is known to be controllable in monolithic silicon processing. However, for large currents, Iout, the value of Rsense has to be relatively small so as to limit the voltage drop across Rsense; too large a voltage across Rsense often limits the working voltage of the system. Therefore, to make the value of Rsense low, Rsense has to be either made up of a physically large set of many parallel resistors as shown in FIG. 2 (Related Art) or has to be made with a material having inherent low resistance. If Rsense is made physically large such as shown in FIG. 2, the metal interconnects, depicted as “Rconnect,” become quite resistive compared to the desired value of Rsense and it becomes difficult to define the actual electrical resistance of Rsense. If a low resistance material is employed, especially if low compared to interconnect lines to Rsense, the actual electrical resistance of Rsense again becomes difficult to define accurately. Another complication is that if Rref is made of the same low value resistance material in order to provide accurate matching, Rref then generally needs to be physically large.
In addition to dealing with these problematical complications, another aspect of this disclosure relates to “Kelvin connections.” Kelvin connections are used compensate for voltage losses caused by line resistances which would otherwise cause errors in low voltage measurements. This is accomplished generally by providing a source line and a measurement line—also referred to commonly as “force line” and “sense line,” respectively—to an interconnection point, known as the Kelvin connection, which is as close to a testing device as possible.